Liquid crystal polymers

ABSTRACT

Liquid crystal polyester derived from phenylene-naphthalene monomers and one or more comonomers display an improved balance of properties, including low melt viscosity, fast cycle time in molding, very low mold shrinkage, high tensile and/or flexural strength, solvent resistance, excellent barrier properties, low water absorption, low thermal expansion coefficient, excellent thermostability, and/or low flammability. The phenylene-naphthalene monomers are  
                 
The one or more comonomers include 4-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, terephthalic acid, isophthalic acid, and derivatives and combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/US03/25910, filed on Aug. 19,2003, which claims priority from U.S. provisional application, Ser. No.60/404,487, filed Aug. 19, 2002. The entire disclosure of bothapplications is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to wholly aromatic liquid crystalline polymers.

BACKGROUND OF THE INVENTION

Liquid crystalline phases (mesophases) are partially orderedintermediate phases existing between the crystalline solid and isotropicliquid Materials in a liquid crystalline phase can flow like liquids,while retaining several features of crystalline solids such as opticaland electromagnetic anisotropy characteristics. These properties are dueto a specific amount of positional or orientational order in theirstructure. Mesogens or mesogenic groups are chemical moieties thatinduce mesophases under certain conditions. According to the ways togenerate a liquid crystalline phase, these groups can be classified aslyotropic (exihibits liquid crystalline phase in solution) andthermotropic (exhibits liquid crystalline phase in melt, a singlecomponent system) liquid crystals.

The two main types of liquid crystalline phases are the nematic andsmectic mesophases. In nematic phases the molecules have only anorientational order, while in smectic phases they have bothorientational and positional order in one or more dimensions.

When a thermotropic LC compound is heated, the solid changes into arather turbid liquid at the melting point. The fluidity may be high fora nematic phase and relatively low for the smectic phases. When observedbetween crossed polarizers under a microscope, the fluid is found to bestrongly birefringent. Upon further heating, another transition point isreached where the turbid liquid becomes isotropic and consequentlyoptically clear (clearing point). Between these two transition points,the liquid crystal phase is thermodynamically stable Both phasetransitions are first order and the latent heat at the clearing point isusually an order of magnitude smaller than the melting point.

The polarizing m is a classical and useful tool for the study of liquidcrystals. Dependent upon the boundary conditions and the type of LCphase, specific textures are observed and used to classify the differentphases.

Liquid crystal polymers were discovered in the 1950s, when Onsager andFlory theoretically predicted that rigid rod-like macromolecules shoulddisplay liquid crystalline properties. An axial ratio of 6.42 is enoughfor a polymer to form an LC melt. However, the molecular weight must behigh to achieve good mechanical properties. The first main chainthermotropic liquid crystalline polymer was reported by Roviello andSirigu in the 1970s, and since then many patents have been published andseveral LC polymers were commercialized.

Compared to monomer liquid crystals, polymer liquid crystals can displaysimilar behaviors, and be classified into thermotropic and lyotropicLCPs. Several well known classes of polymers including polyesters,polyethers and polyamides can exhibit liquid crystalline phases.According to different mesogen positions in the polymer, LC polymers canbe classified as main chain, side chain and combined liquid crystalpolymers. More complex architectures are also possible.

LCPs are quite different from the conventional polymers. They haveproperties that include low melt viscosity, fast cycle time in molding,very low mold shrinkage, excellent mechanical properties, solventresistance, excellent barrier properties, low water absorption, lowthermal expansion coefficient, excellent thermostability, lowflammability, etc. Therefore, they have been explored for numerousapplications in the following areas: high-strength and high-modulusfibers, precision molded small components, films exhibiting excellentbarrier properties, novel composites, processing aids in the melt,reversible information storage, electro-optical displays and non-linearoptical devices.

The mesogenic groups in LCPs are usually rod-like or disk-likemolecules, such as two or more rigid cyclic units. Aromatic rings arethe most common units used in liquid crystal polymer to provide rigidrod structures. The synthesis, structure, rheology, processing,performance and applications of many LCPs have been comprehensivelydescribed in the literature, including Demus, D., et al, PhysicalProperties of Liquid Crystals; Wiley-VCH Verlag GmbH: Weinheim, 1999;Kwolek, S. L. Encycl. Polym. Sci. Eng. 1987, 9, 1-61; Collyer, A. A.;Editor. Liquid Crystal Polymers. From Structures to Applications;Elsevier: London, 1992; Ciferri, A.; Krigbaum, W. R.; Meyer, R. B.;Editor. Polymer Liquid Crystals; Academic Press: New York, N.Y., 1982;and Isayev, A. I.; Kyu, T.; Cheng, S. Z. D.; Editors. Liquid-CrystallinePolymer Systems: Technological Advances. (Symposium at the 209thNational Meeting of the American Chemical Society, Anaheim, California,Apr. 2-7, 1995.) [In: ACS Symp. Ser., 1996; 632]; ACS: Washington, D.C.,1996.

Thermotropic main chain liquid crystal polymers are the most importantgroup of LCPs. They consist of mesogenic groups incorporated into thebackbone of the polymer chain, and when prepared without flexiblespacers, are usually known as wholly aromatic thermotropic LCPs. Becauseof their main chain stiffness and high packing density, they can exhibitexcellent mechanical properties and are extremely useful inhigh-strength and high-modulus fibers. Since they form LC phases whenmelted, the viscosity in the melt state is relatively low, thus make theprocessing easy. Furthermore, the rod-like mesogenic groups can bealigned during the extruding or spinning process and give very highstrength along the fiber direction.

Polyesters are a very important group of this class of polymers.Structures of some commercially important theremotropic copolyesters arelisted in Table 1. TABLE 1 Structures of some thermotropic co-polyestersChemical Structure Monomers 1

p-hydroxybenzoic acid (HBA) 2

4,4′-biphenol (BP)/ Terephthalic acid (TA) 3

6-hydroxy-2- naphthoic acid (HNA)/HBA 4

2-methyl hydroquinone (2- MHQ)/TA 5

Isophthalic acid (IA)/ HBA/BP/TA

Generally, wholly aromatic thermotropic polyesters have poor solubilityin normal organic solvents. Good solvents for this class of polymersinclude fluorinated compounds, such as pentafluorophenol (PFP),p-fluorophenol, trifluoroacetic acid, etc. Due to the poor solubility incommon solvents, GPC data are usually not available in the literature.However, Kinugawa, et al. have investigated the molecular weightdistributions of LC aromatic polyesters by the GPC-low-angle laser lightscattering technique.

General characterization methods for this class of polymers includedifferential scanning calorimetry (DSC), polarized light microscopy, andwide-angle X-ray diffraction.

The ability to show anisotropy and readily induce orientation in theliquid crystalline state leads to materials with great strength in thedirection of orientation, and thus, these polymers have receivedconsiderable attention as high-performance fibers, films and plastics,especially for injection molding applications.

The concept of a melt processable LC polymer is a natural extension ofthe discovery of KEVLAR® at DuPont, which is a wholly aromatic LCpolyamide spun from concentrated sulfuric acid. Ekkcel I-2000(copolyester from p-hydroxybenzoic acid (HBA), terephtalic acid (TA) and4,4′-bisphenol (BP)) was the first melt spinable LC polyester reportedin 1972. It has a melting point around 400° C., which is still too highfor common melt spinning equipment.

In the 1970's and 1980's, aromatic LC polyesters were developed quicklyand many LC polyesters were commercialized during this period. XYDAR®was first commercialized by Dartco Manufacturing Company in 1984 and waslater manufactured by Amoco Chemical Company. It exhibits a meltingpoint above 300° C. The VECTRA® family of LCPs was introduced byCelanese in 1985, with a melting point of 250-280° C.

Since these types of polymers offer a unique combination of properties,they are expected to offer potential solutions to problems whichconventional materials are unable to solve. Currently, industrialactivities are mainly concentrated on main chain thermotropic LCPs forinjection molding applications.

Homopolymers from HBA or 6-hydroxy-2-naphthoic acid (HNA) exhibit highcrystallinity and high melting point (higher than 600° C.). Althoughthey provide excellent mechanical and thermal properties, their highmelting points make them intractable and impractical for any commercialapplications, since they are not melt spinnable or injection moldable.Thus, research has focused on developing new polyesters that have bettertractability (lower melting point) without sacrificing other desirableproperties.

The most common way to achieve this is to disrupt the regular chainstructure. Until now, several methods were found to be effective inlowering the melting point of LC polyesters, such as the introduction ofaliphatic spacer units on the backbone, using monomers with bentstructures (kinks), ring substitution, “swivel” structures, andparallel-offset structures (crankshaft) into the backbone. However, aneed for additional LCP having a desired balance of properties,including T_(g), melting point (T_(m)), tensile strength and/or thermalstability, still exists.

Introducing aliphatic structures can give the backbone more flexibility,which disturbs the packing of the polymer chain and lowers the meltingpoint. Numerous efforts have been made in the LC polyester area usingthis strategy. One example is X7G. By introducing the PET structure intothe polymer, the melting point was lowered to about 230-300° C. Anotherexample is SIVERAS, an LC polyester based on PET, introduced by TorayIndustries, Inc. in 1994. It is melt spinable at 310-320° C.

The major drawback for this strategy is that the aliphatic structurealso decreases the degree of liquid crystallinity and lowers the thermalstability and mechanical properties dramatically. The properties aredecreased in proportion with the length of the flexible spacer and itscontent in the polymer.

Instead of using para-substituted monomers, meta- or ortho-substitutionon the phenyl ring will introduce a bent structure into the backbone,thus disturbing the packing and lowering the melting point. An exampleof this is Ekonol, which is composed of units derived from monomers HBA,TA, BP and a small amount of isophthalic acid (IA). The polymer exhibitsvery high tensile modulus and strength as a fiber. The problem with thisstrategy is that the kink structure can not exceed a specific amount inthe total composition, without loss of LC properties. It was reportedthat for kink units having a 120′ core angle such as isophthalic acid,the polymers will not exhibit liquid crystallinity with more than 60 mol% of kink units of the acids. For kink units having a 60′ core angle,the maximum ratio is 30-40 mol %. As the amount of the kinking componentincreased, the liquid crystallinity and the orientability of thepolyesters from the melt decreased. Therefore, the level of tensile andflexural properties decreased. Very high plastic and tensile propertieswere only possible when the kink component was less than 10 mol %.

Introducing a substituent in the aromatic ring can cause a decrease incrystallinity and hence a drop of the melting point of the polyester.The substituents, especially asymmetrical substituents, can disturb thepacking of the chain by inter-chain separation and by the randomarrangements called internal copolymerization effect.

Different substituents, including halogens (Cl and Br), methyl, phenyl,and phenoxy, have been investigated for their effects on lowering themelting point. The size, the additional degrees of rotational andconformational freedom of the substituent has a great effect on how muchthe melting point can be lowered. This approach can also result incomplete loss of LC behavior. If the percentage of the substituent istoo high, this may disturb the packing and the polymer may lose all LCproperties in the melt.

The “swivel” structure is shown below. Since the two phenylene rings arenot in the same plane, they are twisted at a small angle with respect toeach other, and the packing density of the polymer is lowered. Thelinkage “X” can be a direct bond, S, O, etc. Since the disturbinginfluence is along the backbone axis, the risk of losing LC propertiesis normally high, except in the case of a direct bond. This is due inpart to the “kink” which is imparted by the O or S bond.

The simplest “swivel” structure is biphenol (BP), in which there is adirect linkage between the two rings. The liquid crystallinity of thepolymers will not be completely lost even at 100 mol % of BP of thediols. The small twist angle of BP does have an effect on lowering themelting point. For example, Ekkcel I-2000 in which BP is one of theco-monomers, the melting point is more than 200° C. lower thanhomopolymer of HBA.

The common monomer used in this strategy is 6-hydroxy-2-naphthoic acid(HNA). The 2,6-naphthalene ring structure introduces a crankshaftstructure in the polymer chain. After this modification, the meltingpoints are lowered without sacrificing significant crystallinity sincethe backbone is still parallel to the original axis. Therefore, the LCproperties and mechanical properties can be maintained even with arelatively high percentage of HNA monomer.

One of the most prominent high performance LCP polyesters developed wasVECTRA®, derived from HNA and HBA. It is melt processable with commonprocessing equipment capable of handling materials with melting pointsat 250-280° C. The excellent properties of VECTRA® polymers make themuseful in a variety of applications such as optical fiber cables,fishing line and high strength fiber reinforced composites, etc.

From the discussion above, we can see that the introduction of “swivel”and “crankshaft” structures into the backbone of LC polymers are two ofthe best strategies to achieve low melting point for main chain LCpolyester while maintaining excellent mechanical and thermal properties.Therefore, in order to obtain even better tractability and excellentmechanical properties, and investigate their structure-propertyrelationships, wholly aromatic LC polyesters containing aphenylene-naphthalene structure would be desirable.

Although some compounds containing the phenylene-naphthalene structurehave been reported, no polymers containing this subunit have beendescribed in the scientific or patent literature.2-(4-Hydroxyphenyl)naphthalene-6-carboxylic acid is disclosed in U.S.Pat. Nos. 5,151,549 and 5,146,025, but no description of any polymersprepare from the monomer appear in either patent.

Phenylene-naphthalene monomers are useful monomers for themotropic LCpolyesters, as they may introduce additional dissymmetry into theirmonomers and polymers, combine the “crankshaft” and “swivel” effectstogether, and maintain wholly aromatic backbone structure. Therefore,better tractability can be achieved without sacrificing mechanical andliquid crystal properties.

SUMMARY OF THE INVENTION

It has been unexpectedly discovered that wholly aromatic thermotropic LCpolyesters containing the phenylene-naphthalene moiety may be preparedfrom monomers of formula:

Copolyesters from these monomers exhibit superior physical andmechanical properties, including low melt temperatures.

DETAILED DESCRIPTION OF THE INVENTION

The wholly aromatic thermotropic LC polyesters of the present inventionare composed of structural or repeating units of formula I, II, III,and/or IV.

The repeating units may be derived from any monomer having thephenylene-naphthalene structure and appropriate substituents, includingCOOH/ OAc, COOPh/OH, and COOCH₃/OAc. Acid/alcohol (COOH/OH) substituentsare not considered appropriate, as reaction rates of such monomers arerelatively low, and polymerization may result in a product that iscontaminated with water. Particularly useful monomers are shown below.These are designated A-A, A-B, B-A and B-B, according to the acetoxy andcarboxy substituents on the naphthalene and phenyl rings, respectively.

The LC polyesters may include repeating units in addition to thoseabove, including those derived from monomers such as 4-hydroxybenzoicacid, 2-hydroxy-6-naphthoic acid, 4-aminobenzoic acid, 4-carboxy-4′hydroxy-1.1′-biphenyl, terephthalic acid, isophthalic acid, phthalicacid, 2-phenylterephthalic acid, 1,2-naphthalene dicarboxylic acid,1,4-naphthalenedicarboxylic acid, 2,6-naphthalene dicarboxylic acid and4,4′-biphenyldicarboxylic acid or derivatives such as acetates or estersthereof. 4-Hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, terephthalicacid, and isophthalic acid are preferred comonomers. The LC polymers mayalso include end units derived from compounds such as resorcinol,hydroquinone, methyl hydroquinone, phenyl hydroquinone, catechol,4,4′-dihydroxybiphenyl, and/or acetaminophen.

The LC polyesters may be prepared by any suitable condensation orstep-growth polymerization process; however, melt polycondensation is apreferred method. Industrial processes for LC polymerization typicallydo not utilize direct esterification between diacid and diol monomers,because reaction rates can be slow, and it can be difficult to removewater completely, as noted above. Accordingly, preferred methods for thesynthesis of LC polyesters are alcoholysis, esterolysis, acidolysis andphenolysis, as depicted in Scheme 1. The acidolysis method is used forthe manufacture of many commercial main-chain LCPs. Acetic acid isreleased as the by-product.

In the phenolysis process, the phenyl ester of the aromatic acid is usedinstead of the aromatic acid. This reaction eliminates phenol as theby-product. Compared with acidolysis, the rate of the phenol formationis relatively slow, and it is more difficult to remove phenol thanacetic acid. In the esterolysis method the acetate esters are used andmethylacetate is the by-product. Alcoholysis uses readily availablestarting materials. Its by-product, methanol, is relatively non-toxicand easy to remove.

The polymerization may also be carried out in solution. High boilingsolvents, such as Aroclor-7133, Therminol-66 and Marlotherm-S may beused as heat transfer fluids to carry out the transesterificationreactions. This method can eliminate certain side reactions that mayoccur in melt polycondensation reaction. However, it may also change themorphology and/or thermal transition of the products. The polymersobtained from this method typically yield lower number- andweight-average molecular weights than those from the meltpolycondensation reaction.

For the acidolysis method, diacetate derivatives of the aromatic dioland/or acetoxy derivatives of the aromatic acids are reacted witharomatic dicarboxylic acids in the melt. The polymerization temperatureis typically between 250° C. and 300° C., depending on differentmonomers. The condensation by-product in this reaction is acetic acidand is usually removed by distillation, then vacuumed at hightemperature during the final stage of the polymerization. Catalysts forthe reaction include acetates of sodium, potassium, magnesium, zinc,manganese, cobalt, and antimony (III) oxide.

In one embodiment, the present invention relates to a process forpreparing a liquid crystal polymer. The process includes polymerizingone or more phenylene-naphthalene monomers selected from the groupconsisting of

and combinations thereof, and, optionally, one or more comonomers. Theone or more comonomers may be 4-hydroxybenzoic acid,2-hydroxy-6-naphthoic acid, terephthalic acid, isophthalic acid,hydroquinone, derivatives thereof or a combination thereof.

Monomers containing the phenylene-naphthalene structure may besynthesized by a Suzuki cross-coupling reaction, as shown in Scheme 2.

wherein R¹ and R² are independently carboxy, acyloxy, or hydroxy; and R³is hydroxy, alkoxy or aryl.

A preferred embodiment of this process is shown in Scheme 2A

wherein R¹ and R² are independently carboxy, acyloxy, or hydroxy; and R³is hydroxy, alkoxy or aryl. In particular, R¹ and R² may be carboxy andacetoxy, respectively, both acetoxy, or both carboxy.

Boronic acids are the common substrates in this reaction, along witharyl halides or triflates. Esters of boronic acids and arylboranes arealso used. The most commonly used catalyst istetrakis(triphenylphosphine) palladium(0). Other palladium catalystshave also been employed with success. This reaction requires basesduring the coupling, and the best results are achieved with the use of arelatively weak base such as sodium carbonate. Other bases such assodium hydrogen carbonate, triethylamine and thallium hydroxide are alsoeffective. The suggested mechanism by Suzuki for this reaction is asfollows: First, an oxidative addition of the catalyst to the aryl halidegives an intermediate Ar[Pd]X. Secondly, a transmetallation step yieldsa diarylated palladium moiety. Finally a reductive elimination from thediarylated palladium compound gives the biaryl product and thepalladium(0) catalyst re-enters the catalytic cycle

The LC polymers of the present invention are useful as high-strength andhigh-modulus fibers, and as high-performance films and plastics,especially for injection molding applications.

Experimental

Material and Instruments

4-Methoxybenzene boronic acid and 4-carboxyphenyl boronic acid werepurchased from Lancaster and Frontier Scientific, Inc.2-Bromo-6-methoxynaphthalene was purchased from Lancaster and Aldrich.Triphenylphosphine (99%) was purchased from Lancaster. 1-Propanol,pentanone, acetic anhydride, palladium acetate and hydrobromic acid (48%water solution) were purchased from ACROS. All materials were used asreceived without purification.

Proton nuclear magnetic resonance spectra (¹H NMR) were recorded on aVarian 500 spectrometer and referenced with respect to residual solvent.Elemental analyses were carried out by Midwest Microlab, LLC,Indianapolis, Ind. 46250. GC-MS spectra were obtained by ShimadzuGCMS-QP5000 gas chromatograph mass spectrometer. IR spectra wereobtained from a Bio-Rad FTS 3000MX Mid-IR Excalibur spectrometer.Melting points were measured in capillary with a Mel-Temp apparatus andthe thermometer was not calibrated. Thermogravimetric analysis (TGA)tests were carried out on a Perkin-Elmer TGA 7 with N₂ purging at aheating rate of 20° C./min. Differential scanning calorimetry (DSC)tests were carried out on a Perkin-Elmer DSC 7 and a TA Instruments DSC2920 with N₂ purging at a heating rate of 10° C./min. Melting pointswere recorded as peak temperatures. The liquid crystalline behavior ofthe compounds was studied using polarized microscopy (Nikon EclipseE600) with crossed polarizers, equipped with a heating stage (LinkamTHMS-600). The magnification used was normally 100 or 200×.

Synthesis of 2-methoxy-6-(4′-methoxyphenyl)naphthalene (DMPN)

In an 100 mL three-necked RB flask equipped with a magnetic bar, acondenser and a nitrogen gas inlet, 2-bromo-6-methoxynaphthalene (7.32g, 30 mmol), 4-methoxybenzene boronic acid (4.86 g, 32 mmol) and1-propanol (50 mL) were mixed and stirred at room temperature forapprox. 30 min. Palladium acetate (0.02 g, 0.09 mmol),triphenylphosphine (0.07 g, 0.27 mmol), Na₂CO₃ solution (2M, 18 mL, 36mmol) and water (10 mL) were added and the mixture was refluxed for 1.5h. When the mixture was still hot, 30 mL of water was added and themixture was stirred and cooled to room temperature. The resultantcrystals were filtered, washed with water and recrystallized fromacetone to give the DMPN title compound as colorless flakes (6.86 g,86%). mp 194-196° C. (DSC 196° C). ¹H

NMR (500 MHz, CDCl₃) δ 3.88 (s, 3H), 3.95 (s, 3H), 7-8 (m, 10 H). IR(KBr) ν (cm⁻): 3058 (Ph-H, w), 1028 (OCH₃, s). Anal. Calcd for C₁₈H₁₆O₂:C, 81.79; H, 6.10. Found: C, 81.80; H, 6.25. GC-MS (m/z) 264 (M⁺).

Synthesis of 2-acetoxy-6-(4′-acetoxyphenyl)naphthalene (DAPN)

A mixture of DMPN (2.54 g, 10 mmol), hydrobromic acid (48% watersolution, 40 mL) and acetic acid (40 mL) was purged with nitrogen andrefluxed overnight. The mixture was poured into 200 mL of water and theresultant solid was filtered and dried.2-Hydroxy-6-(4′-hydroxyphenyl)naphthalene was obtained as a light purplesolid (2.20 g, 96%). The crude intermediate was stirred with 40 mL ofacetic anhydride and 1-2 drops of sulfuric acid for 2 hours. Theresultant pink solid was filtered and recrystallized from acetone toafford the title compound as light yellow crystals (2.75 g, 90%). mp178-180° C. (solid-turbid liquid), 205-206° C. (clear point); DSC 182°C. and 207° C. ¹H NMR (500 MHz, CDCl₃) δ 2.29 (s, 3H), 2.33 (s, 3H),7.2-8.3 (m, 10H). IR (KBr) ν (cm⁻¹): 1755 (C═O, s), 1368 (CH₃CO, s),1200-1249 (O—C—O, s). Anal. Calcd for C₂₀H₁₆O₄: C, 74.99; H, 5.03.

Found: C, 74.88; H, 5.02. GC-MS (m/z) 320 (M⁺).

Synthesis of 2-(4′-carboxyphenyl)-6-methoxynaphthalene (CMPN)

In an 100 mL three-necked RB flask equipped with a magnetic bar, acondenser and a nitrogen gas inlet, 2-bromo-6-methoxynaphthalene (4.74g, 20 mmol), 4-carboxybenzene boronic acid (3.50 g, 20 mmol) and1-propanol (40 mL) were mixed and stirred at room temperature forapproximately 30 min. Palladium acetate (0.014 g, 0.003 equiv., 0.06mmol), triphenylphosphine (0.047 g, 0.009 equiv., 0.18 mmol), Na₂CO₃solution (2M, 12 mL, 1.20 equiv., 24 mmol) and water (8 mL) were addedand the mixture was refluxed for 1.5 h. When the mixture was still hot,25 mL of water was added and the mixture was stirred and cooled to roomtemperature. The resultant crystals were filtered, washed with water andrefluxed with 50 mL of acetic acid for 34 h. A white solid was obtained(5.08 g) and recrystallization from acetone showed the title compound aswhite crystals (4.63 g, 83%). mp 288-289° C. ¹H NMR (500 MHz, DMSO) δ3.90 (s, 3H), 7.2-8.3 (m, 10H), 12.99 (s, 1H). IR (KBr) ν (cm⁻¹):2500-3000 (COO—H, very broad, m), 1030 (OCH₃, s), 1678 (C═O, s). Anal.Calcd for C₁₈H₁₄O₃: C, 77.68; H, 5.07. Found: C, 77.56; H, 5.08.

Synthesis of 2-(4′-carboxyphenyl)-6-acetoxynaphthalene (CAPN)

A mixture of CMPN (2.78 g, 10 mmol), hydrobromic acid (48% watersolution, 80 mL) and acetic acid (150 mL) was purged with nitrogen andrefluxed for 48 hours. The mixture was then poured into 400 mL of waterand the resultant purple solid was filtered and dried (2.58 g, 98%). Thecrude intermediate was stirred with 40 mL of acetic anhydride and 1-2drops of sulfuric acid for 2 hours. The resultant solid was filtered(2.88 g) and recrystalization from acetone or pentanone afforded thetitle compound as light yellow crystals (2.02 g, 66%). mp 254-256° C.(DSC 262° C.). ¹H NMR (500 MHz, DMSO) δ 2.34 (s, 3H), 7.3-8.4 (m, 10H),13.02 (s, 1H). IR (KBr) ν (cm⁻¹): COO—H (2800-3100, broad, m), 1685(C═O, s), 1225 (C—O—C, vs), 1365 (CH₃CO, s). Anal. Calcd for C₁₉H₁₄O₄:C, 74.50; H, 4.61.

Found: C, 74.28; H, 4.59.

Synthesis of 6-(4′methoxyphenyl)-2-naphthoic acid (MCPN)

In an 100 mL three-necked RB flask equipped with a magnetic bar, acondenser, and a nitrogen gas inlet, 6-bromo-2-naphthoic acid (2.62 g,96%, 10 mmol), 4-methoxy-benzeneboronic acid (1.52 g, 10 mmol) and1-propanol (20 mL) were mixed and stirred at room temperature for about30 min. Palladium acetate (0.007 g, 0.003 equiv., 0.03 mmol),triphenylphosphine (0.024 g, 0.009 equiv., 0.9 mmol), Na₂CO₃ solution (2M, 8 mL, 1.20 equiv., 12 mmol) and water (4 mL) were added and themixture was refluxed for 2 h. When the mixture was still hot, 20 mL ofwater was added and the mixture was stirred and cooled to roomtemperature. The resultant crystals were filtered, washed with water andrefluxed with 50 mL of acetic acid for 3-4 h. A white solid was obtained(2.55 g) and recrystallization from acetone gave the title compound aswhite crystals (2.24 g, 81%): mp 267-269° C. ¹H NMR (500 MHz, DMSO) δ3.83 (s, 3H), 7.0-8.6 (m, 10H), 13.03 (s, 1H). IR (KBr) ν (cm⁻¹):2800-3100 (PhCOO—H, broad, m), 1690 (C═O, s), 1034 (OCH₃, s). Anal.Calcd for C₁₈H₁₄O₃: C, 77.68; H, 5.07. Found: C, 77.41; H, 5.02.

Synthesis of 6-(4′-acetoxyphenyl)-2-naphthoic acid (ACPN)

A mixture of MCPN (2.78 g, 10 mmol), hydrobromic acid (48% watersolution, 80 mL) and acetic acid (150 mL) was purged with nitrogen andrefluxed for 48 hrs. The mixture was then poured into 400 mL of waterand the resultant purple solid was filtered and dried (2.53 g, 96%). Thecrude intermediate was stirred with 40 mL of acetic anhydride and 1-2drops of sulfuric acid for 2 hours. The resultant solid was filtered(2.91 g) and recrystallization from acetone or pentanone afforded thetitle compound as light yellow crystals (2.18 g, 71%). mp 256-258° C.(DSC 260° C.). ¹H NMR (500 MHz, DMSO) δ 2.31 (s, 3H), 7.2-8.7 (m, 10H),13.1 (s, 1H). IR (KBr) ν (cm⁻¹): 2800-3100 (PhCOO—H, broad, m), 1686(C═O, s), 1364 (CH₃CO, s). Anal. Calcd for C₁₉H₁₄O₄: C, 74.50; H, 4.61.Found: C, 74.53; H, 4.59.

Synthesis of 2-carboxy-6-(4′-carboxyphenyl)naphthalene (DCPN)

In an 100 mL three-necked RB flask equipped with a magnetic bar, acondenser and a nitrogen gas inlet, 6-bromo-2-naphthoic acid (2.51 g, 10mmol), 4-carboxybenzene boronic acid (1.66 g, 10 mmol) and 20 mL of1-propanol were mixed and stirred at room temperature for about 30 min.Palladium acetate (0.007 g, 0.003 equiv., 0.03 mmol), triphenylphosphine(0.024 g, 0.009 equiv., 0.9 mmol), Na₂CO₃ solution (2 M, 8 mL, 1.20equiv., 12 mmol) and water (4 mL) were added and the mixture wasrefluxed for 1.5 h. When the mixture was still hot, 20 mL of water wasadded and the mixture was stirred and cooled to room temperature. Thesolid was separated by filtration and refluxed with 2 mL of 1M HCl and25 mL of acetic acid. A white solid was obtained after filtration. Nomelting point was detected up to 350° C. ¹H NMR (500 MHz, DMSO) δ7.9-8.7 (m, 10H), 13.1 (s, 2H). IR (KBr) ν (cm⁻¹): Anal. Calcd forC₁₈H₁₂O₄: C, 73.97; H, 4.14. Found: C, 73.59; H, 4.05.

Suzuki Coupling Reactions

The reaction conditions of Huff et al.(Org. Synth. 1988, 75, 53-60) wereused in our coupling reactions. The reactions were carried out in1-propanol and water. Sodium carbonate was used as the base, andtriphenylphosphine and palladium acetate were used to generate Pd(0) insitu. The temperature was around 100° C. for refluxing. Typically,reactions were completed within one hour. The solution was darkred-orange in color at the end of the reaction and the products wereprecipitated from the solution even at refluxing temperature. Aftercooling to room temperature, the mixture was filtered and washed withwater to give crystals or powders. For compounds containing an acidgroup, the resultant products were sodium salts of the acid.Acidification with acetic acid gave the acid products. The results aresummarized in Table 2.

An easy and common way to cleave the aryl methyl ether group is byrefluxing the substrates overnight in hydrobromic acid solution. Thismethod worked well for the A-A monomer (Scheme 3). For A-B or B-Amonomers, the solubilities are much lower than the A-A monomer andextended reaction times (24-48 hours) were required to complete thedemethylation process. From the NMR spectra, the uncleaved compound wasless than 3% in the crude product. The yields were very good (above95%). These cleaved compounds were used in the next step after workupwithout further purification.

TABLE 2 A—A A-B B-A B—B R₁ OMe OMe COOH COOH R₂ OMe COOH OMe COOH Yield*(%) 85-90 80-85 80-85 75-80*Isolated yield after recrystallization

The acetylation reaction was carried out in acetic anhydride withsulfuric acid as catalyst. The reactions were performed at roomtemperature or at 40-50° C. for 2-3 hours. The yields were nearlyquantitative.

The resultant products were usually pink powders, and recrystallizationgave fine, light yellow or pink crystals. The structures of pureproducts were confirmed by NMR, IR, GC-MS and elemental analysis. Forthe A-A monomer, the GC-MS showed a molecular ion peak with m/z=320(EI), which matched the calculated molecular weight of the molecule.

Almost all the monomers and intermediates showed liquid crystal phaseswhen heated. The liquid crystal properties were investigated bycapillary melting test, DSC and cross polarized microscope. Transitiontemperatures were determined by the peak temperatures from DSC curves.The data is listed in Table 3 (Cr=crystal, N=nematic, I=isotropicliquid). TABLE 3 Structures and transition temperature for monomersSample ID Structures Transition Temperature Shao-01-01

Cr 196 I(I 187 N 142 Cr) Shao-01-06

Cr 288 N 338 I Shao-02-27

Cr 296 N 322 I Shao-01-10

Cr 269 N 339 I Shao-01-46

Cr 316 N 416 I Shao-01-21

Cr 182 N 207 I Shao-01-18

Cr 270 I Shao-01-54

Cr 263 N→polymerization Shao-01-63

Cr 260 N→polymerization Shao-01-16

No melting point was detected up to 350° C.

2-methoxy-6-(4′-methyoxyphenyl)naphthalene (Shao-01-01) did not show anyliquid crystal phase during heating process, however nematic phase wasobserved during cooling (monotropic liquid crystalline phase). The A-Amonomer (Shao-01-21) melted at around 180° C. into a turbid liquid(nematic liquid crystal phase), and turned into a clear liquid at 206°C. A-B and B-A monomers (Shao-01-54 and Shao-01-63) melted to nematicphase, however the clearing point was not observed up to decompositiontemperature because the polymerization occurs at higher temperatures.The B-B monomer's melting point was very high and was not observed up to350° C. However, under fast heating rate (40° C./min), an endothermalpeak was observed on the DSC curve at around 420° C., which is quiteabove its decomposition temperature.

Some of the DSC curves of the monomers showed two endothermal transitionpeaks when heated. The enthalpies for the second peaks (clearing points)were much smaller than that for the first peaks (melting points).

Under polarized light microscope, threaded textures were commonlyobserved when the monomers melted. These textures are typical texturesfor nematic liquid crystalline phases.

The thermal stability of all monomers was investigated by TGA at aheating rate of 20° C./min under N₂ atmosphere. The temperature at 5%and 10% weight loss were used to characterize the thermal stability andthe results are summarized in Table 4. TABLE 4 TGA data of monomers 5%weight loss 10% weight loss Sample ID temperature (° C.) temperature (°C.) Shao-01-01 182 199 Shao-01-06 220 233 Shao-01-10 253 270 Shao-01-21195 208 Shao-01-54 230 250 Shao-01-63 240 257

The entropy and enthalpy changes at transition temperatures (at Tg andTm) are measured or calculated from DSC curves and listed in Table 5.TABLE 5 Entropy and enthalpy at transitions for monomers At MeltingPoint At Clearing Point ID Structures (J/g) (J/g) Shao-01-01

ΔH = 130.2 ΔS = 0.28 N/A Shao-01-06

ΔH = 113.8 ΔS = 0.20 ΔH = 26.2 ΔS = 43 × 10⁻³ Shao-01-27

ΔH = 84.7 ΔS = 0.15 ΔH = 4.8 ΔS = 8.1 × 10⁻³ Shao-01-10

ΔH = 102.8 ΔS = 0.19 ΔH = 19.0 ΔS = 31 × 10⁻³ Shao-01-46

ΔH = 96.8 ΔS = 0.16 ΔH = 2.1 ΔS = 3.0 × 10⁻³ Shao-01-21

ΔH = 111.7 ΔS = 0.22 ΔH = 3.5 ΔS = 7.5 × 10⁻³ Shao-01-18

ΔH = 100.8 ΔS = 0.19 N/A Shao-01-54

ΔH = 87.7 ΔS = 0.16 N/A Shao-01-63

ΔH = 72.1 ΔS = 0.13 N/A

Compared to other monomers with the same functional groups but differentcore structure, we can see that as the rigid rod length increases, theLC temperature range also increases (Table 6 and Table 7). Aninteresting point is that CMPN and MCPN have almost the same clearingtemperature (338 and 339° C.), indicating that the LC phase stabilitiesare almost the same for these two compounds. However, the melting pointof MCPN is nearly 20 degrees lower than CMPN. TABLE 6 Transitiontemperatures for some monomers Transition Temperatures MonomersStructures (° C.) 6-methoxy-2-naphthoic acid

Cr 206 N 219 I 4′-methoxy-4- carboxybiphenyl

Cr 258 N 300 I 2-(4′carboxyphenyl)-6- methoxy naphthalene (CMPN)

Cr 288 N 338 I 6-(4′-carboxyphenyl)-2- naphthoic acid (MCPN)

Cr 269 N 339 I

For the diacetoxy compounds in Table 7, the similar effect was observed.When the core structures are naphthalene and biphenyl, the molecules donot show any liquid crystalline behavior. The phenylene-naphthalenestructure monomer began to show nematic phase by providing longer rigidrod length. However, when compared to symmetric monomer6,6′-diacetoxy-2,2′-bianphthyl, both the melting point and clearingpoint of dissymmetric phenylene-naphthalene monomer were much lower.TABLE 7 Transition temperatures for some monomers TransitionTemperatures Monomers Structures (° C.) 2,6-diacetoxynaphthalene

Cr 175 I 4,4′-diacetoxybiphenyl

Cr 161 I 2-acetoxy-6-(4′- acetoxyphenyl)naphthalene (DAPN)

Cr 182 N 207 I 6,6′-diacetoxy-2,2′-binaphthyl

Cr 246 N 304 IMaterials and Instruments—Synthesis of Polymers

Potassium acetate (KOAc), tin (II) trifluoromethane sulfonate((CF₃SO₃)₂Sn), phenyl acetate, pentafluorophenol (PFP) andpentafluorobenzene (PFB) were purchased from Acros. Tetrachloroethylene(TCE) was purchased from Aldrich. 2-acetoxy-6-naphthoic acid (ANA),4-acetoxy benzoic acid (ABA) were purchased from Proctor. Benzoic acidwas purchased from Fisher. 6-Acetoxy-2-naphthoic acid (ANA),4-acetoxybenzoic acid (ABA) were purchased from Proctor. Terephthalicacid (TA) was purchased from Amoco. A heat transfer fluid, Therminol 66,was obtained from Solutia, Inc. The dispersing agent, Ganex V-220, wasobtained from ISP Tehnologies, Inc. All materials were used as receivedwithout purification.

GC-MS spectra were obtained on a Shimadzu GCMS-QP5000 gas chromatographmass spectrometer. TGA tests were carried out on a Perkin-Elmer TGA 7with N₂ purging at heating rate of 20° C./min. DSC tests were carriedout on a Perkin-Elmer DSC 7 and a TA Instruments DSC 2920 with N₂purging at a heating rate of 10-20° C./min. Some samples were tested onMettler-Toledo DSC 822e at a heating and cooling rate of 20° C./min.Thermo mechanical analysis (TMA) tests were carried out on aPerkin-Elmer TMA 7 with He purging at a heating rate of 10° C./min. Theliquid crystalline behavior of the compounds was studied using polarizedmicroscopy (Nikon Eclipse E600) with crossed polarizers, equipped with aheating stage (Linkam THMS-600). The magnification used was 100 or 200×.

Synthesis of Polyesters: Bulk Polymerization

The monomers and approximately 500 ppm of KOAc were charged into apolymerization tube with a side branch. The system was degassed andpurged with nitrogen three times. While purging with nitrogen, thetemperature was increased to 250° C. for about 1.5 h, 280° C. for 30min, 300° C. for 30 min, and 320° C. for 30 min. During the temperaturegradient, acetic acid was collected in a test tube at the end of theside branch. At the final stage, while the reaction temperature was keptat 320-330° C., the side branch was sealed and vacuum was slowlyconducted for 30-60 min to remove the acetic acid byproduct.

In most cases, the monomers melted at 220-230° C., and polymerizationoccurred with the evolution of acetic acid at around 250° C. Aftercooling to room temperature, the reaction vessel was broken and theresultant polymer was collected.

Synthesis of Polyesters: Non-Aqueous Dispersion Polymerization

In an 100 mL RB flask, the monomers (for an example, 0.612 g of CAPN,0.540 g of ABA) and the catalyst (500 ppm) were mixed with dispersingagent, Ganex V-220 (0.045 g), and heat transfer oil, Therminol 66 (8.0ml). The mixture was heated to 220-250° C. for about 2 h with N₂ purgingand stirring. The temperature was then increased to 280° C. for 30 min,300° C. for 30 min and 320° C. for 30 min.

After cooling to room temperature, the resultant polymer (powder solid)was isolated and extracted with hexane overnight and dried.

Inherent Viscosities of Polymers

Inherent viscosities (IV's) of polymers were measured in PFP/PFB mixedsolution (w/w=1.46/1) at 30° C. with an Ubbelohde viscometer. Theweighed polymer was dissolved in heated PFP. PFB was added and mixedcompletely. IV's were measured at a polymer concentration ofapproximately 0.2 g/dL in the mixed solvent system. The solution wasfiltered with a 1 μm filter before filling the viscometer.

Results and Discussion: Synthesis of Polyesters

Effect of Catalyst—KOAc and Sn(OTf)₂

For the polymerization, two different catalysts were studied with themodel reaction of esterification of benzoic acid and phenyl acetate at150° C. to compare their efficiency (Scheme 3.2). One catalyst is KOAc,which is commonly used in industry. The other is Sn(OTf)₂, is reportedto be efficient for polymerization of lactones at low temperature. Theconcentration of the catalyst was 500 ppm. The two starting materialswere charged into the flask at 1:1 ratio with the catalyst, and thereaction mixture was heated to 150° C. under stirring. The reaction wasmonitored by GC-MS at 1 hr, 2 hr and 4 hr.

The results from these two catalysts are listed in Table 8. After fourhours, the product peak was still very small for the reaction that usedKOAc as the catalyst. For the reaction using (CF₃SO₃)₂Sn as thecatalyst, the product peak was quite large after only one hour. After 4hr at 150° C., conversion of starting materials to phenyl benzoate wasgreater than 95%. Therefore, the preliminary study demonstrated that(CF₃SO₃)₂Sn is an effective catalyst for the acidolysis reaction and iseffective at lower temperatures (150° C.) than the commonly used KOAc.

However, at higher temperatures (250° C., the starting polymerizationtemperature), it was difficult to operate the polymerization with thetin catalyst. The high activity of the tin catalyst at low temperaturescauses premature homopolymerization of the lower melting monomer.4-Acetoxybenzoic acid melts at 187° C. and 2-acetoxy-6-naphthoic acidmelts at 228° C. Thus, melting of the lower melting point monomer in thepresence of a catalyst active at low temperatures can induce significanthomo-polymerization. Blocky structures can be formed and, in some cases,the melting points of the oligomers formed may increase beyond thepolymerization temperature, causing solidification of the polymerizationmixture. For the system using KOAc as the catalyst, significantpolymerization began at around 250° C. At this temperature the startingmaterials are a well mixed solution. KOAc is easy to use in hightemperature polymerizations and was used in subsequent polymerizations.However, the tin catalyst may be useful when used in lowerconcentrations. TABLE 8 Catalyst effect for model reaction CatalystAfter 1 hour After 2 hours After 4 hours No catalyst Only startingmaterial Only starting material Only starting material peaks peaks peaksKOAc Only starting material Small product peak Small product peak peaksArea_(p)/Area_(a) = 0.006 Area_(p)/Area_(a) = 0.017 (CF₃SO₃)₂Sn Bigproduct peak Big product peak Big product peak Area_(p)/Area_(a) = 7.2Area_(p)/Area_(a) = 13.7 Area_(p)/Area_(a) = 28.7Area_(p): the peak area of product, M/Z = 198 (M⁺)Area_(a); the peak area of benzoic acid, M/Z = 122 (M⁺)Polymerization Method

Two different polymerization methods were studied: bulk polymerizationand non-aqueous dispersion polymerization.

(I) Bulk Polymerization Without Stirring

The bulk polymerization was conducted in a polymerization tube with aside branch. Usually monomers melted at 220-250° C. to form a clearyellow solution. Polymerization occurred around 250° C. and acetic aciddistilled out of the reaction. Some sublimation of the monomer wasobserved at the beginning as the vapor condensed on the glass tube andthe solid was washed down by the refluxing acetic acid. The bubblingaction of the acetic acid helped with the mixing of the monomers. Thepolymerization tube was also shaken occasionally to ensure that a goodmixture formed. For some compositions, the mixture solidified during thelater stages of polymerization due to the high melting point of theproducts.

A Vectra-type LCP (HBA/HNA=58/42) were synthesized using this procedureas a control experiment. IV's as high as 5.1 were measured (usually thecommercial VECTRA® has an IV around 5.0), which demonstrated that thismethod worked very well for this polymerization and produced highmolecular polyester. IV's ranging from 1.8 to 6.7 dL/g were obtained forthe soluble polymer compositions investigated in this thesis.

(II) Non-aqueous Dispersion Polymerization

Non-aqueous dispersion polymerization was also studied as a method toproduce polyesters, with Therminol 66 synthetic heat transfer fluid as adispersion medium. This is made from hydrogenated terphenyls andpolyphenyls, and offers outstanding high-temperature performance up to345° C. Ganex V-220 was used as a dispersing agent.

All of the starting materials were stirred and heated in a 3-neckedround bottom flask. The mixture turned into a clear orange solution atapproximately 250° C., and after 30-40 mins of polymerization, somepowder began to participate from the solution and the mixture becamecloudy. For some reactions, the polymer stuck to the magnetic stirringbar. The final product was usually a grey powder and was washed byhexane.

The TGA curves for the polymer showed two main weight losses. One ofthem was around 250° C., which indicated that the polymerization was notcompleted. One possible reason for this is that a vacuum stage was notused for this reaction and the complete removal of acetic acid neededeven higher temperatures or longer times. DSC curves for the productswere inconsistent, which may be caused by the incomplete removal of theheat transfer fluid or dispersing agent. Therefore, this method was notchosen for polymer synthesis.

Molecular Weight and Solubility of Polymers

Most of the synthesized polyesters are not soluble in any organicsolvent, even hot pentafluorophenol (PFP). The best solubility wasobtained from HNA/TA/DAPN co-polyesters. When the polyesters from thisseries had a melting point lower than 260° C., solubility in PFP/PFBmixed solvent was obtained. When the polymer had a higher melting pointit was not soluble, although many polymers could still be swollen inheated pure PFP. The solubility of many polymers incorporatingphenylene-naphthalene structures was lower than the commercial VECTRA®polymers. The majority of the polymers synthesized in this thesis werenot soluble in hot PFP.

The inherent viscosity (IV) data for all soluble copolymers ranged from1.8 to 6.7 dL/g, which is in the same range of VECTRA® polymers(approximately 3-5). This indicated that the polyesters were preparedwith relatively high molecular weights. It was also found that higherIVs were obtained from A-B or B-A systems rather than the A-A or B-Bsystems, which was also true for VECTRA® polyesters. The stiochiometryis easier to control in A-B and B-A systems, which might be the reasonfor higher IV values. Alternatively, chain stiffness and thecorresponding Mark-Houwink constants may vary in these systems, whichwould cause different IV values for the same molecular weights.

Thermal Properties of Polyesters

Polyesters from A-A monomer

A-A monomer (DAPN) was copolymerized with HBA and TA to give a hard andbrittle brown solid, which was not soluble in common solvents. The molarpercentage of DAPN was between 15-30%. The thermal property results fromthe polyesters are listed below (Table 9). Most of the polymers were notsoluble even in hot PFP, and the only soluble polymer(HBA/TA/DAPN=45/27.5/27.5) had an IV of 1.8 dL/g. One possible reasonfor its higher solubility may be the lower molecular weight, asindicated by the IV. The thermal stability for these polyesters was verygood with most of the decomposition temperatures above 420° C. TABLE 9Properties of HBA/TA/DAPN copolyesters

Composition IV^(a) 5% weight 10% weight Sample ID HBA/TA/DAPN (dL/g)loss T(° C.) loss T(° C.) Tg(° C.) Tm(° C.) Shao-01-120 75/15/15 NS 460480 — 387 Shao-01-109 60/20/20 NS 450 470 — 358 Shao-01-67 50/25/25 NS430 460 110˜120 347 Shao-02-58 45/27.5/27.5 1.8 420 440 115˜120 353Shao-02-170 45/27.5/27.5 NS 439 455 — 351 Shao-01-152 40/30/30 NS 420460 — 346 Shao-02-174 36/32/32 NS 407 442 — 352 Shao-02-79 35/32.5/32.5NS 415 435 — 372 Shao-01-118 30/35/35 NS 450 480 — 390^(a)IV was obtained in pentaflorophenol and pentaflorobenzene mixture at30° C.^(b)NS means not soluble in the mixed solvent

The melting points (Tm) of this series of polymers were relatively high.The lowest melting point was above 340° C., which was obtained with 30%DAPN. Either increasing or decreasing DAPN from 30% will generate higherTm for the copolymers. Glass transition temperatures (Tg) were notobvious on the DSC curves, and the shape of melting peak appeared quitesimilar to VECTRA® polymers, which was broad and small.

Some of the copolyesters were selected for annealing studies at 250° C.and 280° C. at different times. After annealing, the sample was retestedby DSC. The results showed no significant change for these curves. Themelting points shifted slightly to higher temperatures (less than 10°C.), and the shape looked slightly sharper. After annealing at highertemperature (280° C.), these effects became more pronounced. At longerannealing times, the melting peaks split into two clearly defined peaks,which indicated that the polymers have two different transitionprocesses. Previous reports about VECTRA® polymers referred to these twotransitions as slow transition and fast transition. It was also reportedthat the high melting peak remained at the same temperature, which wasindependent of annealing time while the low melting peak shifted to ahigher temperature with increasing annealing time and the enthalpyincreased as well. This was also true for the polyesters studied in thisproject.

Surprisingly, when the HBA monomer was replaced by HNA, the meltingpoints of the polyesters dropped dramatically, to even lower than 240°C. (Table 10). The lowest melting point was obtained with 17% DAPN asco-monomer. Compared to the curve of HNA/TA/HQ, the minimum meltingpoint is 50-60 degrees lower. Surprisingly, some low melting pointcompositions displayed sharp melting peaks. Furthermore, the solubilityof the polyesters improved greatly and most of the compositions could bedissolved or swelled in the mixed solvent of PFP and PFB. Onlypolyesters having high DAPN composition (>30%) did not dissolve at all.TABLE 10 Properties of HNA/TA/DAPN copolyesters

Composition IV^(a) 5% weight 10% weight Sample ID HNA/TA/DAPN (dL/g)loss T(° C.) loss T(° C.) Tg(° C.) Tm(° C.) Shao-02-159 74/13/13 Swells424 436 116 322 Shao-02-146 70/15/15 Swells 418 431 111 307 Shao-02-15866/17/17 2.3 418 438 109 230 Shao-02-145 60/20/20 3.4 416 432 112 233Shao-02-161 56/22/22 3 430 444 112 235 Shao-02-144 50/25/25 2.9 420 435113 259 Shao-02-147 40/30/30 NS^(b) 430 445 113 326 Shao-02-149 30/35/35NS 426 448 112 380^(a)IV was obtained in pentaflorophenol and pentaflorobenzene mixture at30° C.^(b)NS means not soluble in the mixed solvent

The thermostability for these polymers was high, with decompositiontemperatures varying at only a narrow range for the differentcompositions (418-430° C.).

From the DSC curves, an obvious glass transition (Tg) can be observed atapproximately 110-120° C., which is quite similar to the Tg ofcommercial VECTRA®) (110-115° C.). The enthalpy change at the meltingpoint was between 1.3-2.2 J/g. The obvious Tg transition indicated thatcompared to the HBA/TA/DAPN copolyesters, HNA/TA/DAPN copolyesters havea much higher percentage of amorphous structure. This is consistent withthe higher solubility and lower melting points. All of this informationsuggests that HBA structure packs much better than HNA structure withthe DAPN structure.

Polyesters from B-A Monomer

The B-A monomer (ACPN) was copolymerized with HBA or HNA, respectively.Similar to the previous series, the copolymers from HNA have much lowermelting points than those of the HBA copolymers. The properties ofHNA/ACPN copolyesters were summarized in Table 11. The compositions ofACPN were between 25-35 mol %, and most of the polymers have highdecomposition temperatures (above 420° C.). Only one polymer was solublein the mixed solvent of PFP/PFB, and an IV of 6.7 dL/g was obtained.This IV is much higher than the polymers from A-A monomer, possibly dueto the better 1:1 stiochiometric ratio in A-B system than A-A/B-Bsystem, thus producing higher molecular weight polymers. TABLE 11Properties of HNA/ACPN copolyesters

Composition IV^(a) 5% weight 10% weight Sample ID HNA/ACPN (dL/g) lossT(° C.) loss T(° C.) Tg(° C.) Tm(° C.) Shao-02-137 75/25 —^(b) 378 394 —352 Shao-02-105 70/30 6.7 425 438 — 268 Shao-02-244 67.5/32.5 NS^(c) 373385 — 270 Shao-02-115 65/35 NS 420 432 — 268 Shao-02-107 60/40 — 426 440— 260 Shao-02-118 55/45 — 430 445 — 273 Shao-02-109 50/50 NS 420 436 —276 Shao-02-110 40/60 — 425 438 — 301^(a)IV was obtained in pentaflorophenol and pentaflorobenzene mixture at30° C.^(b)— means solubility was not attempted^(c)NS means not soluble

The melting points of these polymers were between 260° C. to 350° C. Thelowest melting point (˜260° C.) was obtained with approximately 37 mol %ACPN monomer. Compared with the HNA/HBA curves, the shape of the meltingpoint-composition curve is sharper, and the lowest melting point alsoshifted to lower compositions of ACPN%. The melting peaks shown on DSCcurves were broad, similar to Vectra's melting peak. The averageenthalpy change at Tm was around 2.8 J/g, which is larger than theprevious series. Tg was not clearly detectable on the DSC curves.

The next series of polymers investigated were the HBA/ACPN copolyesters.The experiental data are shown in Table 12. Interesting DSC curves wereobtained when the HNA monomer from the previous series was replaced bythe HBA monomer. A large sharp endothermal peak was observed between200-210° C. for the HBA/ACPN copolyesters. This peak appeared for mostof the compositions, except for those with ACPN>80%. For ACPN=70%, thefirst endothermal peak was very small. Analysis by hot-stage microscopyshowed that a fluid phase was not formed at these temperatures. In fact,changes in the sample could not be detected optically or by shearing thecover slip over the powdered sample. TABLE 12 Properties of HBA/ACPNcopolyesters

Composition IV 5% weight 10% weight Sample ID HBA/ACPN (dL/g) loss T(°C.) loss T(° C.) Tg(° C.) Tm(° C.) Shao-02-88 70/30 NS^(a) 395 408 214391 Shao-02-95 65/35 —^(b) 415 425 208 386 Shao-02-94 60/40 — 405 420209 384 Shao-02-89 50/50 NS 430 445 206 373 Shao-02-263 45/55 345 380198 363 Shao-02-99 40/60 — 410 420 206 366 Shao-02-265 30/70 — 380 408195 353 Shao-02-103 30/70 — 420 435 181 343 Shao-02-266 25/75 — 390 411197 357 Shao-02-163 20/80 — 417 445 — 381 Shao-02-181 10/90 — 428 452 —383 Shao-02-258  0/100 — 400 417 — 383^(a)NS means not soluble^(b)— means solubility was not attempted

After several tests by different techniques, such as x-ray, DSC anddielectric measurements, it was concluded that the transition was acrystal-crystal transition. It is obvious that this temperature is stillfar above the sharp endothermal peak temperature (200˜220° C.) found inthis work. At the low molecular end of the oligomers studies, thetetramer of HBA had a melting point of 260° C.

Since a Tg transition was not observed around 100-120° C., thepossibility that the 200-210° C. peak represented the Tg wasinvestigated. Wunderlich et al. have reported on hysteresis effects inpolymer glasses that can lead to glass transition temperatures, whichappear as endothermal “peaks” in the DSC curves. The appearance of theTg is often a complex function of the thermal history of the polymersample. Generally, the “peak” appearance results from a superheatedglass that moves quickly toward equilibrium as soon as the time scale ofthe heating permits. DSC tests were performed at different heating ratesfor Shao-02-88, which had the composition of HBA/ACPN =70/30. As theheating rate decreased, the endothermal peak became decreasinglysmaller. This behavior is consistent with hysteresis effects seen inpolymer glasses at Tg.

This polyester was also heated to 400° C. and dropped immediately intodry ice. The quenched sample was checked by DSC test again at 10°C./min. Because of the rapid cooling rate, the polymer chains do nothave time for better packing, and more amorphous phase forms. Thequenched sample showed a typical Tg transition at around 200° C.

An annealing study for this polymer was also performed at 300° C. for 12hours. After annealing, the first endothermal peak shifted slightly tolower temperature, and the entropy was smaller (ΔH=7.25 J/g→6.36 J/g)than the sample without annealing. Meanwhile, the melting peak becamelarger ((ΔH=2.8 J/g→4.1 J/g), as compared to the unannealed polymer.Annealing of other compositions gave similar results. The annealingusually increases the crystallinity of the polymer.

DMTA is a sensitive method to detect Tg transitions. The storage moduluswill decrease and the loss factor, tan δ, will show a peak at the Tgtransition. However, since the melting point for these copolyesters wasaround 400° C., it was difficult to make coherent film from hotpressing. A sample of thickness around 0.8-1 mm was obtained from hotpressing and subjected to TMA testing. The analysis was conducted inpenetration mode under a static force of 50 mN at a heating rate of 10°C./min. There are two important results from this test. First, it isquite evident that there is not a Tg in the 100-120° C. range where mostwholly aromatic polyesters show a Tg. Second, the penetration resultseen at >200° C. is strongly indicative of the Tg.

A TMA expansion test was also conducted with a static force of 0 mN at aheating rate of 10° C./min. There are three different slopes on thecurves. The initial slope is about 4×10⁻³, and after the Tg transition(220-230° C.), the slope changed to approximately 1×10⁻⁴. The finalslope on the curve increased to about 0.8. These results are consistentwith the current assignments of the Tg and Tm in the copolyester series.

in conclusion, a combination of thermal methods demonstrated that thesharp endothermal peak at approximately 210° C. is a Tg transition. TheTg transition temperatures from these methods were in good agreementwith each other (200-230° C.). Most surprisingly, this Tg assignment isalmost 100° C. higher than reported for other wholly aromaticpolyesters.

A melting point-composition diagram for this series indicates that asthe content of the ACPN monomer increased, the melting point of thecopolyemers decreased, typical of the eutectic behavior observed in LCpolyesters. However, the polyester melting points increased abruptly atACPN concentrations above 70 mol % and remained constant at 383° C.

Polyesters from A-B Monomer

A-B monomer (CAPN) was copolymerized with HBA and HNA, respectively.Similar to the B-A monomer, the copolymers with HNA have much lowermelting points than the HBA copolymers. The polyesters from HNA/CAPNhave similar thermal properties to HNA/ACPN copolymers, i.e., a minimummelting point at approximately 260° C. (Table 13) with a CAPNcomposition around 35%. Compared with HNA/HBA copolymers, the shape ofthe curve is quite similar, and the only difference is that the minimummelting point was achieved with lower ACPN% than HBA%. Select sampleswere subjected to solubility testing, but were not soluble in hot PFP.Therefore, IV data was not obtained. TABLE 13 Properties of HNA/CAPNcopolyesters

Composition 5% weight 10% weight Sample ID HBA/ACPN IV loss T(° C.) lossT(° C.) Tg(° C.) Tm(° C.) Shao-02-126 80/20 NS^(b) 414 428 — 325Shao-02-133 75/25 NS 394 406 — 278 Shao-02-120 70/30 NS 425 438 ˜115 264Shao-02-135 65/35 —^(a) 400 414 — 249 Shao-02-199 65/35 — 401 415 — 260Shao-02-203 63/37 — 390 412 — 270 Shao-02-121 60/40 NS 414 424 ˜120 275Shao-02-201 60/40 — 393 412 — 267 Shao-02-198 55/45 — 412 427 — 261Shao-02-207 55/45 — 388 408 — 267 Shao-02-125 50/50 NS 418 433 — 287Shao-02-208 45/55 — 413 430 ˜115 293^(a)— means solubility was not attempted^(b)NS means not soluble

The Tg transitions were barely perceptible in the DSC curves, and themelting point peaks were broad and small. The enthalpy changes at themelting points were around 2.0-5.6 J/g, which is also very close to thatof HNA/ACPN polymers.

Copolyesters from HBA/CAPN were also synthesized. Their compositions andproperties were listed in Table 14. Solubility was very poor, thereforeIV data was not obtained. This series of polymers produced someinteresting DSC curves. Initially, the most prominent peak in the DSCcurve appeared in the range of 175-210° C. The shape of the curve wassimilar to the shape of the DSC curves for the HBA/ACPN copolymers. Itappears that hysteresis effects are also present in this series, andoccasionally further complicated by relaxation effects near the Tg. Asdiscussed previously, this behavior is a complex function of theprevious thermal history on both heating and cooling conditions. When afaster heating rate (40° C./min) was used and the final temperature wasincreased to 460° C., a second endothermal peak appeared above 400° C.,which is believed to be the melting point. The enthalpy change at themelting point was around 4.7-11.2 J/g, which is much higher than otherseries. Additionally, the Tg shape appeared similar to that describedearlier for the HBA/ACPN series. TABLE 14 Properties of HBA/CAPNcopolyesters

Composition 5% weight 10% weight Sample ID HBA/CAPN IV loss T(° C.) lossT(° C.) Tg(° C.)? Tm(° C.)^(a) Shao-02-250 80/20 NS 405 425 242 435Shao-02-74 70/30 NS^(c) 420 435 210 440 Shao-02-152 65/35 —^(b) 426 430189 430 Shao-02-251 65/35 — 415 433 191 431 Shao-02-156 55/45 — 409 424163 417 Shao-02-75 50/50 NS 450 460 160 420 Shao-02-260 40/60 — 423 435— 408 Shao-02-267 30/70 NS 420 434 — 413 Shao-02-270 20/80^(a)Temperature was taken from DSC test at a heating rate of 40 °C./min.^(b)means solubility was not attempted.^(c)NS means not soluble

In summary, the polyesters from HBA/CAPN were quite similar to thosefrom HBA/ACPN. One noticeable difference was the gradual shift in Tgwith composition. The Tg shifts from 160° C. for the HBA/CAPN=50/50composition to 242° C. for the 80/20 composition. A Tg shift of thismagnitude has not been reported for wholly aromatic copolyesters. Themelting points (420-440° C.) were much higher than those from HBA/ACPN.

Polyesters from B-B Monomer

The diacid monomer had very poor solubility and its melting point wasmuch higher than other monomers (>350° C.). At 250-280° C., the monomerremained as a solid in the melted monomer mixture while the othermonomers had already begun polymerization. As a result, only lowmolecular weight oligomers were produced.

Structure of Polyesters: Powder X-ray Patterns

The polyesters were ultrasonically treated to form a fine powder andx-ray spectra were taken at room temperature. Some of the polyestersshowed very high degrees of crystallinity compared with VECTRA® (typicaldegree of crystallinity: 15-20%). Polyesters from HBA always gave higherdegrees of crystallinity than those from HNA with similar composition,such as HBA/ACPN polyesters (40-45%,), HBA/CAPN polyesters (42-48%) andHBA/TA/DAPN polyesters (30-36%). When the HBA was replaced by HNA, thecrystallinity decreased dramatically, such as HNA/CAPN (20-22%) andHNA/TA/DAPN (15-20%). Qualitatively, the differences can be observedsince the more highly crystalline copolymers usually display severalsharp peaks, while the less crystalline polymers display only a fewpeaks superimposed on an amorphous background. All of the data fromx-ray was consistent with the previous DSC data and conclusions.

Liquid Crystal Behavior

The polyesters were studied under cross polarized microscope for theirliquid crystal behavior and to confirm DSC results. Copolyesters fromHNA/TA/DAPN have low melting points, thus were chosen for thisinvestigation. The threaded texture did not disappear, even at 450° C.All of the polymers investigated in this thesis displayed similartextures and were consistent with classical nematic threaded textures.

In summary, different composition copolymers were synthesizedsuccessfully by copolymerization of TA, ABA or ANA with newphenylene-naphthalene monomers. The polymerization was carried out inbulk and at temperatures in the range of 250-330° C., and liquidcrystalline polyesters with a relatively high molecular weight andthermal stablility were obtained. The composition greatly affected theproperties of polymers.

Solubility of these polymers was very poor. Only a small number ofpolymers could be dissolved in PFP/PFB solution. The IV's were between1.8 and 6.7 dL/g. Polyesters from all hydroxy-acid monomer systemsshowed poorer solubility and higher IV than those from systemsincorporating diols.

The diacetoxy monomer, DAPN, was copolymerized with HBA or HNA and TA.The HBA copolymers showed much higher degrees of crystallinity andmelting points, and lower solubilities than the HNA copolymers. TheHNA/TA/DAPN polyesters were found to have even lower melting points thanthe commercial VECTRA® compositions.

The A-B (CAPN) and B-A (ACPN) monomers were copolymerized with HBA orHNA. These two series of polymers showed similar properties. HBAcopolyesters showed unusually high Tg transitions which was confirmed byvarious TMA tests. HNA copolyesters showed much lower melting pointsthan those of HBA copolyesters. The major difference between A-B and B-Aseries is the orientation of the ester bonds along the polymer chain.This also affected the polymer properties. For example, HBA/ACPNpolymers showed a Tg at around 210° C., while the Tg's of HBA/CAPNpolymers were 160-240° C. Their melting points and degrees ofcrystallinity were also quite different.

Some compositions showed degrees of crystallinity greater than 40%,which is very unusual for wholly aromatic LC polyesters. To ourknowledge, these are some of the highest Tg's reported for whollyaromatic copolyesters to date.

In summary, the phenylene-naphthalene structure shows effects oflowering the melting points of polymers. Several series of polymers fromHNA show even lower melting points than VECTRA® polymers. Also, someunexpected results were obtained, such as high Tg and high crystallinityof HBA copolymers.

Large Scale Synthesis of Copolyesters from A-A Monomer

As the HNA/TA/DAPN copolyesters provide the lowest melting points, andthe monomer can be made from the least expensive starting materials,this composition was chosen for scale-up and fiber property evaluation.Monomers (HNA/TA/DAPN=60/20/20, 69.0 g of HNA, 16.6 g of TA and 32.0 gof DAPN) and catalyst KOAc (200˜300 ppm) were charged into a 3-neckedround bottom flask equipped with a mechanical stirrer, and a nitrogeninlet and outlet. The system was degassed and purged with N₂ threetimes. While stirring and purging with N₂, the temperature was increasedto approximately 250° C. for 1.5-2 hours, 280° C. for 1 hr, 300° C. for30 min. The vacuum was slowly introduced and lasted for 1-2 hr. Whencooled to room temperature, the flask was broken and light brown hardsolid was obtained.

Inherent viscosities (IV) of polymers were measured in a PFP/PFB (w/w=1.46/1) mixed solution at 30° C. with an Ubbelohde viscometer. Theweighed polymer was dissolved in heated PFP first, and then PFB wasadded and mixed completely, with concentrations of approximately 0.2g/dl. The solution was filtered with 1 μm filter before filling theviscometer.

Two batches of polyesters were synthesized in larger scale with the samecomposition (HNA/TA/DAPN=60/20/20). The first batch had a lower inherentviscosity (IV=3.0 dL/g), while the second batch experienced a longertime under vacuum at the final stage of the polymerization, and thus hada higher IV (3.9 dL/g).

Polyester Fibers

The granulated polymers were dried for several days. Before spinning,they were cold pressed into rods 4-7 cm in length and about 1 cm indiameter. Different spinning conditions were studied for both of thepolymers. The results are listed in Table 15.

For Polyester I, the fiber broke occasionally when the Grid temperaturewas equal to or lower than 300° C. However, for grid temperature of 310°C. and 280° C. for pack temperature, stable fiber spinning was observed.The extrusion rate (through put) for most spinning trials was 0.3cc/min. The fiber could be collected at 600-800 revolutions per minute(RPM) without substantial breaking of the fiber line. Therefore theseoptimized conditions were used for spinning polyester I. TABLE 15 SpinConditions for Polyester I* Grid Pack Grid Pack RPM Spin TemperatureTemperature Pressure Pressure (meters/ # (° C.) (° C.) (psi) (psi) min)1 300 270 185 70 800 2 280 260 385 70 600 3 280 250 447 700 800 4 280250 985 380 600 6 310 280 221 280 600 7 310 280 268 810 800*Polyester I: HNA/TA/DAPN = 60/20/20, IV = 3.0 dL/g

For polyester II, the first and second spinning trials were notsuccessful. Some un-meltable impurities blocked the hole and continuousfiber was not obtained. The granulated polymer particles were put intotetrachloroethylene, which has a density of 1.6 g/cm³ and stirred, andallowed to stand for 10 minutes. The majority of the polymer particleswere floating on the top of the solvent, and some pieces of glass wereat the bottom of the solvent. The separated polymer was dried againbefore spinning.

Mechanical tests of the fibers were conducted at Ticona. All tests wereconducted at 50% room humidity (RH) and at 23° C. The average denier wascalculated from the weight of 10 or 15 cm fils per sample. 10 tests wereconducted for each sample and the reported numbers were their averagevalues. The gauge length was 10 inches.

Mechanical test data for polymer I is listed in Table 16. Most of themodulus values are around 610-640 g/denier, which are approximately thesame as VECTRA® polymers (˜600 g/denier).

However, the break tenacity and break elongation were 3-5 g/denier and0.7-0.9% respectively, somewhat lower than VECTRA® polymers (˜10g/denier and 1-2%). I-I and I-7 had lower modulus values, and the testdata were slightly more scattered, indicating that some of the singlefibers were weak. Many factors can influence the tenacity andelongation-to-break values including impurities, spinning conditions,polymer molecular weight, etc. Although it is impossible to study all ofthe parameters in a limited number of spinning trials, we suspect thatthe molecular weight (IV) of this batch of polymers may be the majorfactor related to these values. TABLE 16 Mechanical properties of singlefiber (as spun) Spin Modulus Break Tenacity Break Number Denier ^(a)(g/denier) (g/denier) Elongation (%) I-1 3.60 502.60 3.28 0.71 I-2 3.00631.90 4.27 0.72 I-3 4.20 614.90 4.02 0.70 I-4 4.80 524.60 3.70 0.76 I-65.40 642.70 5.17 0.87 I-7 4.80 483.40 3.32 0.73^(a) Denier: gram per 9000 meters

The results indicate that this polymer can be spun into good fibers witha grid temperature of 310° C. and a pack temperature of 280° C. Themechanical modulus of these fibers is similar to or slight higher thanthe VECTRA® polymers. However, the tenacity modulus and break elongationwere lower.

1. A liquid crystal polymer comprising at least one repeating unitselected from the group consisting of radicals of formula I, II, and IV:

and combinations thereof.
 2. A liquid crystal polymer according to claim1, wherein said at least one repeating unit is derived from aphenylene-naphthalene monomer selected from the group consisting of

and combinations thereof, and, optionally, one or comonomers.
 3. Aliquid crystal polymer according to claim 2, wherein saidphenylene-naphthalene monomer is


4. A liquid crystal polymer according to claim 2, wherein saidphenylene-naphthalene monomer is


5. A liquid crystal polymer according to claim 2, wherein saidphenylene-naphthalene monomer is


6. A liquid crystal polymer according to claim 2, wherein saidphenylene-naphthalene monomer is


7. A liquid crystal polymer according to claim 2, wherein the one ormore comonomers are selected from 4-hydroxybenzoic acid,2-hydroxy-6-naphthoic acid, terephthalic acid, isophthalic acid,hydroquinone, derivatives thereof and combinations thereof.
 8. A liquidcrystal polymer according to claim 2, wherein the one or more comonomersis 4-hydroxybenzoic acid or derivatives thereof.
 9. A liquid crystalpolymer according to claim 2, wherein the one or more comonomers are2-hydroxy-6-naphthoic acid or a derivative thereof.
 10. A liquid crystalpolymer according to claim 2, wherein the one or more comonomers areterephthalic acid or a derivative thereof.
 11. A liquid crystal polymeraccording to claim 2, wherein the one or more comonomers are isophthalicacid or a derivative thereof.
 12. A liquid crystal polymer according toclaim 2, wherein the one or more comonomers are hydroquinone or aderivative thereof.
 13. A liquid crystal polymer according to claim 2,comprising repeating units of formula


14. A liquid crystal polymer according to claim 2, comprising repeatingunits of formula


15. A liquid crystal polymer according to claim 2, comprising repeatingunits of formula


16. A liquid crystal polymer according to claim 2, comprising repeatingunits of formula


17. A liquid crystal polymer according to claim 2, comprising repeatingunits of formula


18. A liquid crystal polymer according to claim 2, comprising repeatingunits of formula


19. A compound selected from:


20. A process for preparing a liquid crystal polymer, said processcomprising polymerizing one or more phenylene-naphthalene monomersselected from the group consisting of

and combinations thereof, and, optionally, one or more comonomers.
 21. Aprocess according to claim 20, wherein the one or more comonomers areselected from the group consisting of 4-hydroxybenzoic acid,2-hydroxy-6-naphthoic acid, terephthalic acid, isophthalic acid,hydroquinone, derivatives thereof and combinations thereof.